Organic light emitting diodes (OLEDs) are light emitting diodes (LEDs) where the emissive electroluminescent layer is a film of organic compound(s) that emits light in response to an electric current.
OLEDs are used on a number of display applications, ranging from mobile devices, television displays, and digital cameras, with their use expanding into further potential uses as the technology develops. OLEDs provide certain advantages over traditional lighting solutions, such as incandescent lights, including lighter weights, lower drive voltages, greater energy efficiency higher luminance, wider viewing angles, more flexible displays, ease of recycling, and thinner displays, among others.
OLEDs may be constructed to be comprised of a single layer or multiple layers of materials, depending on the application and particular desired characteristics. For example, the emissive layer may be used individually, in a bilayer structure, or in a trilayer structure, among others. The different layers may include different materials to provide particular characteristics for various reasons (e.g. improved efficiency). OLEDS may be fabricated on a number of different substrates, including, but not limited to, various types of glass and plastic. There may be more than one emissive layer. An example two layer structure could include separate hole transporting and electron transporting layers where the recombination of holes and electrons results in the emission of light.
White OLEDs (WOLEDs) are OLEDs that emit white or near-white light through a variety of methods. A method to emit white or near-white light is to combine different colours of light to formulate white light (e.g. combining red, green and yellow, or various combinations of complementary colors). In particular, complementary colors blue and orange can be combined, in various proportions, to create white or near-white light.
White or near-white light may encompass range of colors—the ‘whiteness’ of the light may be quantified through a term known in the art as ‘color temperature’ which may range from warmer, orange-tinted light at lower color temperatures to colder, blue-tinted light at higher color temperatures (e.g., a higher correlated color temperature (CCT)). Traditional incandescent light sources provide warm orange tinted white light, and white fluorescent tubes and bulbs (including compact fluorescent bulbs) produce colder white light.
WOLEDs may be suitable, in particular, for lighting applications. Alternatives to lighting from incandescent lights may be urgently needed as incandescent types are being phased out in Canada and around the world.
Further, given the strong regulations in the European Union, there is a significant commercial potential in supplying WOLEDs to the international market.
A class of organic materials known as boron subphthalocyanines (BsubPcs) has been explored for use in WOLEDs. The subphthalocyanine of boron contains three repeating isoindoline units whereas all other metal(loid)s form normal phthalocyanines with four isoindoline units.
Subphthalocyanine adopts a non-planar molecular conformation referred to as a bowl. Protruding from the convex side of the bowl is an axial substituent (X or Ra).
The first BsubPc, Cl-BsubPc was isolated in a 1% yield in 1973 and its molecular structure unambiguously determined in 1974. BsubPcs remained unexplored until the 1990s when Kobayashi expanded the chemistry of BsubPcs followed by Torres in the 2000s. Prior to 2007, BsubPcs remained relatively understudied as functional organic electronic materials as they suffered from a lack of reproducible preparatory methods and contradictory evidence regarding their basic properties. Recently, BsubPcs have begun to be applied in functional devices.
BsubPcs has been engineered into many different forms including dyes, sublimates and engineered crystals. However, the vast majority of cases (>90%) use the prototypical Cl-BsubPc, which lacks chemical variation and tunability.
An extensive review of BsubPcs in organic electronic devices highlighting the use of Cl-BsubPc and the need to study other derivatives was published. Other derivatives, for example, phenoxy-BsubPcs, have been found to be easily made and allow for considerable variability including physical and electronic properties.
A new solution is thus needed for overcoming the shortfalls of the materials currently used in the market.